It is generally known, by on arrangement such that cutting operation is performed in a cutting apparatus such as a lathe, planer, and shaper with a cutting tool driven by ultrasonic vibration, that various effects are obtained such as that the cutting resistance is greatly reduced and abnormal vibrations such as chattering are eliminated. As a result, the accuracy in the processing in terms of out-of-roundness, surface roughness, etc. is improved and the cutting tool is prolonged in its life, and further, materials difficult to cut become easy to process.
FIG. 1 shows an example of prior art ultrasonic vibrational cutting apparatus. On a tool rest 1, there is supported a tool shank (tool holder) 5 subjected to bending (flexural) vibration a held in place by a presser plate 2, fastening bolts 3, and a fastening jig 4, in which the fastening jig 4 is arranged such that its legs are located at nodal positions of the tool shank 5. At one end of the tool shank 5, there is fixed a cutting tool 7 to face a workpiece 6. On the side of the other end of the tool shank 5, there are provided an axial vibrator 8 and an amplitude expanding horn 9 joined thereto at the position of loop of the vibrational pattern of the tool shank 5 as indicated by single-dot chain lines.
In the ultrasonic vibrational cutting apparatus arranged as aforesaid, when the axial vibrator 8 is driven by an ultrasonic oscillating device (not shown), the tool shank 5 vibrates as indicated by the single-dot chain lines in the figure and thereby the edge of the cutting tool 7 undergoes an ultrasonic vibration in the cutting direction and exhibits the above described vibrational cutting effects. More specifically, by representing the cutting speed of the workpiece 6 by v, the vibrating frequency of the vibrational cutting tool 7 by f, and the amplitude by a, the effects are exhibited under the condition of v&lt;2.pi.fa.
According to the above described arrangement, since the axial vibrator 8 as the source of the ultrasonic vibration can be installed at a position far away from the cutting tool 7, there is an advantage in that the same can be easily installed on a general-purpose lathe.
However, at the contact point of the cutting tool 7 with the workpiece 6, there is produced, other than a principal force P.sub.c acting in the tangential direction toward the workpiece, a radial force P.sub.t acting in the radial direction toward the cutting tool 7. As a result, the resultant P of these forces is applied to the cutting tool 7 and produces harmful abnormal vibrations. Therefore, in many cases, an apparatus providing only a simple vibration in the tangential direction cannot provide satisfactory cutting effects.
Therefore, there are proposed some apparatues, as disclosed, for example, in Japanese Patent Publication No. 50-20289, arranged such that the vibrational cutting is performed therein with the tool shank 5 tilted so that the vibrating direction of the cutting tool 7 will agree with the direction of the resultant cutting resistance P. Namely, as shown in FIG. 3 corresponding with FIG. 1, a tilting table 12 is provided between the tool rest 11 and tool base-plate 10, whereby the tool shank 5 is tilted through an angle .theta., the angle formed between the tangential force P.sub.c and the resultant P. Here, such an angle of inclination .theta. can be obtained by measuring, in FIG. 1, the radial force acting in the direction perpendicular to the vibration of the cutting tool 7 and the force acting in the cutting direction.
By thus bringing the vibrating direction of the cutting tool 7 into agreement with the direction of the resultant resistance force P, no radial force P.sub.t acts in the axial direction of the cutting tool 7 and good vibrational cutting effects can be obtained.
There are, however, some problems with such prior art arrangement, which will be described below. The radial force P.sub.t is variable depending upon cutting conditions, for example, the change in the depth of cutting, or cutting speed, or difference in materials of the work piece. As a result, it becomes necessary, every time the cutting condition is changed, to exchange the tilting table 12 for another one with a different tilting angle, or to use a tilting table 12 whose angle of inclination is variable and adjust the angle. Therefore, if a wide variety of workpieces are to be processed, the setup of the angles becomes very complicated.
With respect to the means for measuring the radial force P.sub.t, many are provided with a stress sensor disposed on the depth-of-cut feed mechanism because generally it is only necessary to detect the stress applied to the cutting tool 7 in the direction perpendicular to the cutting direction. However, if it is desired to monitor the stress acting on the cutting tool 7 during the cutting operation using a prior art apparatus as shown in FIG. 3 with the tool shank 5 tilted, the stress to which the depth-of-cut feed mechanism is subjected is different from the stress perpendicular to the vibration of the cutting tool 7. More specifically, in order that the stress applied to the cutting tool 7 is detected in such a system as shown in FIG. 3, the stress sensor must not be provided on the depth-of-cut feed mechanism, but the stress in the axial line of the tool shank 5 must be measured. However, such a tool shank 5 or the mechanism for holding it constitutes the ultrasonic vibrating system and therefore it is difficult to provide a stress sensor on such a portion.